Rank: Species
Lineage: Bacteria;Tenericutes;Mollicutes;Mycoplasmatales;Mycoplasmataceae;Mycoplasma;Mycoplasma genitalium
Description: Mycoplasma. This genus currently comprizes more than 120 obligate parasitic species found in the wide spectrum of hosts, including humans, animals, insects and plants. The primary habitats of human and animal mycoplasmas are mucouse membranes of the respiratory and urogenital tracts, eyes, mammary glands and the joints. Infection that proceeds through attachment of the bacteria to the host cell via specialized surface proteins, adhesins, and subsequent invation, results in prolonged intracellular persistence that may cause lethality. Once detected in association with their eukaryotic host tissue, most of mycoplasmas can be cultivated in the absence of a host if their extremely fastidious growth requirements are met. All mycoplasmas are phenotypically distinguished from other bacteria by their small size (0.3-0.8 micron in diameter) and lack of a cell wall. The latter is one of the major trait that puts them in the separate taxonimic group of microorganisms, class Mollicutes (Latin mollis, soft; cutis, skin). The cell membrane is rich in protein (up to two thirds of the membrane mass) that to a great extent consists of highly structurally adaptive lipoproteins employed in evading the host immune system, attachment to the host cells and pathogenic invasion. Most mycoplasmas are non-motile, with exception of a few flask-shaped human and animal pathogens (M. pneumoniae, M. genitalium, M. gallisepticum, M. pulmonis and M. mobile). Motile mycoplasmas glide over surfaces by an unknown mechanism that is suspected to employ actin-like cytoskeletal component as well as motility proteins unique for this microbial group. Cell division proceeds via normal binary fission or via elongation of a parent cell to multinucleate filaments and subsequent breakup to coccoid bodies.Mycoplasmas carry the smallest genomes of self-replicating cells (less than 500 recognizable coding regions), which is one of the reasons they were among the first microorganisms selected for the genome-sequencing projects. The complete sequence of the genome of M. genitalium was the second to be reported following closely the report on the complete sequence of the Haemophilus influenzae genome. Examination of the mycoplasmal genomic data indicates the biochemical pathways where gene reductions took place, and helps define the set of genes essential for a minimal self-replicating cell. During their evolution, mycoplasmas appear to have lost all the genes involved in amino acid and cofactor biosynthesis, synthesis of the cell wall and lipid metabolism, resulting in the requirement of the full spectrum of the substrates and factors taken up from the host or from the complex artificial culture medium. They have lost the number of genes involved in cellular processes, such as cell division, heat shock response, regulatory genes, the two-component signal transduction systems, histidine protein kinases or their target response regulators, and most transcription factors. Majority of mycoplasmas are deficient in genes coding for components of intermediary and energy metabolism and thus depend mostly on glycolysis as an ATP-generating pathway.
Reference Material:
https://www.ncbi.nlm.nih.gov/genome/?term=Mycoplasma%20genitalium
